Timeout exception occurs frequently when getting data by Bulk APIs

Hi all,

I always get data of Account and Contact serially by Bulk APIs.

When getting Contacts after completing to get Accounts, I always get timeout exception until I wait over 5 minutes and try again. But it would not happen if I get only Contacts .

Is there any asset or connection thing need to be released manually when export of a kind of data completed?

Any suggestions?

Thanks,

Biao